<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>响应式原理</title>
    <style>
        .container{
            height: 100px;
            background:pink;
            text-align: center;
        }

        @media screen and (max-width<799px){
            .container{
                width: 100%;
            }
        }

        @media screen and (min-width>799px){
            .container{
                width: 980px;
            }
        }

        @media screen and (min-width>1000px){
            .container{
                width: 1180px;
            }
        }

        @media screen and (min-width>1200px){
            .container{
                width: 1200px;
            }
        }
    </style>
</head>
<body>
    <div class="container">
            我是内容
    </div>
</body>
</html>